In Vitro Rumen Fermentation and Microbial Enzyme Activities Influenced by Vitamin B_(12) Supplementation in Different Concentrate to Forage Ratios

This study was conducted to investigate the effects of vitamin B12 supplementation in diets with different concentrate to forage ratios on in vitro rumen fermentation and microbial enzyme activities.The trial was carried out using fermentation in vitro with the combinations of three concentrate to forage ratios(corn meal∶Chinese wildrye=35∶65,50∶50 and 65∶35) and three supplemental doses of vitamin B12(0,40 and 90 ng/mL) in a 3×3 factorial design.Rumen fluid was collected from three Hu sheep fitted with permanent rumen fistula.Rumen fermentation parameters and microbial enzyme activities were determined at 24 h incubation in vitro.The results showed as follows: 1) with the increasing of concentrate to forage ratio and supplemental doses of vitamin B12,gas production,potential gas production and organic matter digestibility at 24 h incubation in vitro were enhanced significantly(P0.01),and vitamin B12 supplementation had a linear dose response relationship in them(P0.01).2) When the concentrate to forage ratios were 50∶50 and 65∶35,the concentrations of ammonia nitrogen,microbial protein,total volatile fatty acids,acetate and propionate were significantly increased(P0.05) by vitamin B12 supplementation except the butyrate concentration and acetate/propionate(P0.05).3) Activities of carboxymethyl cellulase and xylanase were significantly increased at 40 ng/mL vitamin B12 for the concentrate to forage ratios of 35∶65 and 50∶50(P0.05),while they were significantly increased at 90 ng/mL vitamin B12 for the concentrate to forage ratio of 65∶35 at 24 h incubation(P0.05).The results of this study indicate that the concentrate to forage ratio and vitamin B12 supplementation have effects on in vitro rumen fermentation.Vitamin B12 supplementation can improve organic matter digestibility and production of microbial protein and total volatile fatty acids through enhancing microbial enzyme activities.When the concentrate to forage ratios(corn meal∶Chinese wildrye) are higher(50∶50 and 65∶35),vitamin B12 has pronounced effects on rumen fermentation in a dose-dependent manner.